‘‘It’s a very emotional day. An extremely horrific act happened very near to the ballpark,’’ Nationals general manager Mike Rizzo said. ‘‘Our thoughts and prayers go out to all the victims over there and all the people affected by this. We felt it was inappropriate to play a major league baseball game with such tragedy right down the street.’’

Located just blocks from the Navy Yard, one of the stadium’s parking lots was used for families of the Navy Yard employees to meet following the evacuation of the facility.

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‘‘Major League Baseball mourns those who have been lost to this senseless tragedy,’’ commissioner Bud Selig said. ‘‘Major League Baseball’s security department will continue to track this matter in consultation with the Nationals and under the guidance of the local authorities.’’

The postponement was announced shortly after 3 p.m., about four hours before scheduled start.

With some streets north of the stadium closed, there was heavy traffic on South Capitol Street, parallel to the third-base line. Potomac Street, parallel to first-base line, was blocked by police. Police activity was visible around the stadium, and sirens could be heard throughout the afternoon.